Random "unknown error has occurred" and "connection to server lost"

Nextcloud version (eg, 20.0.5): 20.0.6
Operating system and version (eg, Ubuntu 20.04): Debian 10
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4
PHP version (eg, 7.4): 7.4.16

The issue you are facing:

Shared hosting (IONOS Web Pro).

Randomly, users are experiencing these 2 following errors:

  • unknown error has occurred
  • connection to servr lost

This happens on any app, not only Files, for instance Calendar.

No error message in nextcloud.log.

I could reproduce the error by uploading a 100MB mp4 file using FF 87.0.
I could trace the event and uploaded a HAR file here.
I did not find anything in this log.
The “event” happened at 2021-04-02T10:43:08.

The same upload has been working fine three times at different moments using Brave browser, making me think this might be related to the browser, in some way.

Is this the first time you’ve seen this error? (Y/N): N

The output of your Nextcloud log in Admin > Logging:


The output of your Apache/nginx/system log in /var/log/____:

Nothing in access.log. No access to error.log

Where do you get thos errors?

@rakekniven these errors are displayed in the upper right display of the browser.

Screenshots would be perfect.


It’s in french, the 1st error says: “connection to server lost”, the 2nd says: “unknown error has occurred”.

It’s all in the same display, and the1st disappears within a few seconds, while the 2nd one remains as long as you don’t close it.

1 Like

Hi, I guess I’d rather open a ticket for this…

You should open a ticket with IONOS. Or perahps try a more performant hoster.
At Cloudeezy, you can try to reproduce the same error in their FREE version.

Hi, I don’t know how a hoster would make it work with Brave and not FF…

I use Firefox with my selfhosted Nextcloud Instance on a daily basis and have never experienced such problems. I really doubt that your problem has anything to do with the browser you are using. And even if it were, the root cause of the problem lies almost certainly somewhere else.